The present invention relates to an explicit routing method for altering the normal routing of a packet-flow as described in the preamble of claim 1, related arrangements as described in the preambles of claim 4 and a source node as described in the preamble of claim 7.
Such an explicit routing method is already known in the art, e.g. from the internet document xe2x80x9cINTERNET PROTOCOL, DARPA INTERNET PROGRAM PROTOCOL SPECIFICATIONxe2x80x9d with reference RFC791, published in September 1981 by Internet Engineering task Force (IETF).
Therein a method of explicit routing through an internet network, called loose or strict source routing, is described. A packet-flow is forwarded from a source-node towards a destination node along an explicit path. An explicit path is specified by intermediate network-nodes. The addresses of these intermediate network-nodes are put in the header of each packet of the packet-flow. By putting the addresses of these intermediate network-nodes of the explicit path in the header of each packet, the overhead of each packet is substantially large.
An object of the present invention is to provide an explicit routing method of the above known type but the packet-overhead should be reduced substantially.
According to the present invention, this object is achieved by the method as claimed in claim 1, the arrangements as claimed in claim 4 and the source node as claimed in claim 7.
Indeed, by determination of only those intermediate network-nodes on the explicit path that are necessary to deviate the packet-flow from the hop-by-hop path onto the explicit path the object of the present invention is achieved. As long as a packet-flow is forwarded to a downstream intermediate network-node on the explicit path that also is situated on the hop-by-hop path, the packet-flow will be forwarded without adding the network-node address to each packet, because the common present routing mechanism will handle the forwarding along the hop-by-hop path. Consequently, by adding to the packet address only the explicit specification (of this downstream network-node) necessary to force the packet-flow onto the explicit path, the packet header overhead is reduced substantially compared to the explicit routing method as known in the art.
It is to be noticed that in spite of the fact that the prior art document is situated within the internet area, the invention is not restricted hereto because the present invention can be applied in any packet-based network.
Another characteristic feature of the present invention is described in the appended claims 2 and 5 and is related to the determination of relevant intermediate network nodes.
If the source node has information at its disposal, concerning only the shortest path tree from the source node towards all other network nodes and the destination node, then the shortest path tree is used, by the source node, to determine which network nodes on the explicit path are necessary to deviate the packet-flow from the hop-by-hop path onto the explicit path.
A further characteristic feature of the present invention is described in the appended claims 3 and 6 and are also related to the determination of relevant intermediate network nodes.
If the source node is provided with information concerning the shortest path trees from the source node, from each of the network nodes and the destination node towards all other nodes present within the network, the source node can based hereon determine which network nodes on the explicit path are necessary to deviate the packet-flow from the hop-by-hop path onto the explicit path. The result is optimised compared to the previously described situation, meaning that the number of the to be added network node addresses is reduced or in the worst case the same.